just nattering about this last bit, if the seed coating doesn't contain anything harmful to the seed and the packet is well sealed it doesn't seem to me that it should make any difference at all. i'm thinking that claim may just be a mistake that isn't fully spelled out. to me clay is pretty much inert and too would be food coloring if it supposed to be food safe. and why use food coloring anyways? just marketing stuff to me. perhaps a bit of fertilizer and/or fungicide to try to prevent damping off. ok, go ahead, but finally it's not something too likely to be done by me anyways.
if you want to do your own seed tapes use TP, a bit of soluble glue with a toothpick and dab the TP where you want the seeds to stick and then sprinkle the seeds on there and let it dry. dump off lose seeds and voila!
and no, i've never done this at any significant scale as i'm pretty happy running a seed drill and then using a rake dragged through the line (at 90 degrees) to spread the seeds out more. close enough and done without complicating the issue.
the coated seeds do make a lot of sense if you are a large operation trying to fill seed starting trays with exactly one seed. i've watched those vids and been amazed by how that works (and also the prices for something like a metal plate with certain sized holes drilled in it in a regular pattern).